@pedro if you would post the SQL query that you are using that would be more useful in finding out what are you trying to do and where the issue is. But given the details, the following query would work for your case -

SELECT IdUser, IdProject, IdTool, NULL as IdEval, Status as StatusA, NULL as StatusB
FROM TableA
UNION ALL
SELECT IdUser, IdProject, IdTool, IdEval, NULL as StatusA, Status as StatusB
FROM TableB;